Radio coil construction



Sept. 22, 1936; J, cALAMlTA 2,055,247

RADIO COIL CONSTRUCTION ,2 MW m INVEN TOR. JO$EPH CALAMITA.

ATTOYS.

Sept. 22, 1936 J. CALAMETA 2,055,247

RADIO CQIL CONSTRUCTION Filed July 13, 1935 2 Sheets-Sheet 2 ]A1 mmm mu L W 0 J: c. l :MQW

INVENTOR.

' ATTORN'E JOSEPH CHLAMITA- Patented Sept. 22, 1936 PATENT OFFICE RADIO COIL CONSTRUCTION Joseph Calamita, Roosevelt, N. Y. Application July 13, 1935, Serial No. 31,150

8 Claims.

I This invention relates to improvements in radio inductances, and is particularly concerned with the construction of a unitary multi-band transformer unit adapted for use with radio receiving apparatus.

In the prior art it has been relatively common practice to provide radio frequency transformers of the plug-in type, sothat a radio receiver may be converted for use on divergent wave bands, merely by removing one set of plugin coils, and by inserting another set of plug-in "coils, the other set having Wave band characteristics suitable for the wave band range within'which it is desired to operate. Although apparatus of this type makes a standard receiver relatively flexible in its use, a considerable investment is required in a plurality of sets of plug-in coils, and an unnecessary amount of time may be consumed in unplugging and replugging the various coil sets.

It is therefore an object of this invention to provide a unitary plug-in coil having a plurality 'of inductances, each adapted for a definite Wave band, selectively connectible to' the radio circuit through a multiple contact switch forming part of the coil unit.

Another object is to provide a coil form con- -struction in which the several independent coil windings are spirally wound in pancake form.

Another object is to arrange the supporting structure of the coil form in such a manner that it may be assembled from easily fabricated parts, whereby a minimum of expense will be involved in the manufacture of the unit.

A further object is to so organize the several coil windings in the unit that each, when in operation, is relatively independent, electrically, of

the other, so that the coil, when in operation, is veryefiicient as an inductance.

Still another object is to provide a multi-wave band coil form rotatable on a base, the coil form having mounted thereon an individually adjustable trimming condenser for each coil winding, whereby slight errors in manufacture, and divergent characteristics of the wiring arrangements in the various apparatus in which the coil forms maybe used, may be compensated. The

attainmentlof the above objectives, along with others, will become apparent by an examination of the drawings and by reading the annexed detail description.

In the drawings:

Fig. 1 is a side elevation, with the shield in section, of my radio coil unit;

ventional radio tube or plug-in coil socket. Upon the plug H, a base plate I6 is integrally formed, this plate having an axial bore within which a rod 11 is rotatably mounted. The rod I1 is preferably circumferentially grooved, as shown, to-

ward its lower end, within which groove a set screw 18 engages to hold the rod in place. A spring I9 is inserted in the base plate bore prior to insertion of the rod, to form a positive contact between the rod and a wire leading from the spring l9 to the prong !5. The base plate 18 also carries three radially arranged switch contacts 26, 2| and 22, each said contact comprising a thimble embedded in the base plate, within which thimble a spring 23 and ball 24 are mounted. Each thimble of the contacts 20, 2! and 22 is connected to one or the other of the prongs I2, I3 or l4.

A coil form unit 2-5 comprises a central threaded sleeve 26 having a flange 21 at its lower end, the sleeve being adapted for fitting engagement over the rod I1, and being fixed thereto by means of a through pin 28 passed through drillings in the sleeve and rod. The coil form, however, is assembled as a unit prior to attachment of the sleeve 26 to the rod I1 and is freely rotatable; A bottom disk 29 is first slipped over the sleeve 26, engaging the flange 2'! thereof. This bottom disk is provided with four sets of switch points 30, 3|, 32 and 33, each set consisting of three switch points 34, 35 and 36 adapted for engagement respectively with the balls of the switch contacts 20, 2! and 22.

1 After assembly of the bottom disk 29, a spacer washer 3l-is added, then a coil form disk 38, then a coil form spacer washer 39, then another coil form disk 38, then another spacer washer '31, and so on in the same sequence until a total of eight coil form disks 38 have been assembled. Thereupon, a spacer washer 40 is added and then a top disk 4|. Directly on the top disk 4|, a metal disk 42 is added, over which a thin insulating disk 43 of mica or the like is added, whereupon the whole series of disks and washers are looked upon the sleeve 26 by means of a lock nut 44. It will be noted that the lock nut 44 bears directly upon the metal disk 42 giving intimate electrical contact between the sleeve and the metal disk. Now, a plurality of transformer windings A, B, C and D are wound over the coil form spacer washers 39 and between adjacent coil form disks 38, in pancake or spiral form, Fig. 4 showing these windings of the transformer A. First, a primary winding 45 is spirally wound, preferably with a thread between each convolution of the winding for spacing of the consecutive winding turns, the ends of the primary winding being carried through suitable grooves in the coil form disks to the edges thereof. Thereafter, a few layers of thread may be wound in the slot between the coil form disks and a spiral secondary winding 46 wound in the same manner as the primary winding, the winding ends likewise being carried through suitable grooves in the coil form disks to the edges thereof. A protecting layer of thread may then be wound around the outside of the secondary winding.

It will be realized that the number of winding turns in each of the four transformers A, B, C and D shown will be different from the other, to provide a natural frequency in each transformer suitable for a different wave band. In the case of the transformer D, which is constructed for lower natural frequency, a greater number of winding turns must be used. In order to insert a sufficient number of turns within the limits defined by the diameter of the coil form disks, the turns may be banked two abreast instead of in a single layer as in the other coils. Such bank winding is shown in the bottom coil at 41. The ends of each primary winding such as 45 are carried down and connected to the inner switch points 35 and 35 of one of the corresponding group of switch points 30 to 33, inclusive. The outer end of each secondary winding 46 is carried down to the outer switch point 34 of the corresponding set of switch points 38 to 33, inclusive. The inner end of each secondary winding is connected to the sleeve 28 which forms a common ground.

Screwed to the top disk 4| I provide a plurality of resilient metallic strips 48 spaced peripherally around the edge thereof, each strip being attached to the edge of the disk 4| by means of a screw 49, and each strip likewise being provided with an adjusting screw 58 adapted to bear upon the mica disk 43 to form a small trimming condenser of maximum capacity. By screwing in the adjusting screw 50 the resilient strip is raised from the mica disk 43 to reduce the capacity of the trimming condenser. The outer end of each secondary winding, besides being connected to one of the switch points 34, is likewise connected to one of the resilient strips 48, whereby the trimming condenser formed by the strip 48 and the metal disk 42 is shunted around each secondary winding.

In the use of the coil unit of this invention, the coil may be plugged into the radio receiving set, the coil form 25 being turned so that one set of the switch points 30 to 33, inclusive, is engaged with the contacts 20, 2| and 22, thus placing one of the transformer windings in circuit. The trimming condenser connected to such winding may then be adjusted to compensate against any stray capacity or inductance effects in the receiver as a whole, whereupon the trimming condenser may be left at the then current setting. Similarly, the other transformers of the coil form may be switched in by turning the coil form 25 and the corresponding trimmers adjusted for optimum results.

The coil form unit 25 is preferably enclosed by a suitable cylindrical shield 5| and also by a top cover (not shown), and the red I! may be provided with a knob 52 having a pointer registering against suitable indicia on the top cover, whereby the operator may quickly turn the knob to effect switching of the coil form to choose that wave band upon which he wishes to operate.

In the design of this apparatus, the electrical efliciency of each coil winding has been taken into consideration, and it will be noted that each coil winding is well spaced from each other coil winding and from metallic parts in the assembly which might have the tendency of broadening the frequency band of each transformer. By the pancake or spiral form of coil, a maximum of compactness accrues along with an electrically efficient form of inductance. of force resulting from an energized coil of this form lie close to the windings themselves, so that a minimum of interference results from adjacent inactive coils and from the sleeve and rod 26 and 21, respectively, which are spaced from the inner coil convolutions by virtue of the insulating spacer washers 39. Likewise, the mechanical construction is sturdy and will withstand hard usage and the fabrication of the device may be easily effected with a minimum number of parts, through the fact that the various coil forming elements such as the coil form disks 38, the spacer washers 31 and the coil form spacer washers 39 are similar to effect a minimum number of different forms of elements.

While I have described my invention in detail in its present preferred embodiment, it will be obvious to those skilled in the art, after understanding my invention, that various changes and modifications may be made therein without departing from the spirit or scope thereof. I aim in the appended claims to cover all such modifications and changes.

What is claimed is:

1. In a coil form for a multi-band radio inductance, a plug base havin prongs, a rod coaxial with said base and mounted for rotation therein, a connection from said rod to one said prong, a plurality of spacer washers and coil forming disks alternately stacked in coaxial relationship on said rod, means holding said washers and disks in assembled relation on said rod, a primary winding spirally arranged between alternate pairs of disks, a secondary winding circumscribing the respective primary winding, spirally arranged between the alternate pairs of disks, and a connection from one end of each said secondary winding to said rod.

2. In a coil form for a multi-band radio inductance, a plug base having prongs, a rod coaxial with said base and mounted for rotation therein,

a connection from said rod to one said prong, a

plurality of spacer washers and coil forming disks alternately stacked in coaxial relationship on said rod, means holding said washers and disks in assembled relation on said rod, a primary winding spirally arranged between alternate pairs of disks, a secondary winding circumscribing the respective primary winding, spirally arranged between the alternate pairs of disks, a connection from one end of each said secondary winding to said rod, a plurality of sets of three switch points carried by said coil form, and connections from the other terminal of each secondary winding,

The normal lines 1 and from both terminals of each primary winding, to each switch point of a set thereof.

3. In a unitary multi-band radio inductance having a plurality of coils selectively connectible in the radio circuit, a common connection for a corresponding one end of each coil winding, a metallic plate carried by the inductance unit and connected to said common connection, insulating means covering said plate, a plurality of resilient strips overlying said insulating means, in insulated relation to said metallic plate, said strips being respectively connected to one each of said coil windings at the other ends thereof, and means for adjusting the space relationship of each said strip with respect to said insulating means, whereby a trimming condenser is formed for each said coil.

4. In a multi-band radio inductance, a plug base having prongs and switch contacts connected to said prongs, a coil form rotatably mounted on said base for turning said coil form comprising a bottom plate, a plurality of alternately arranged spacer washers and coil forming disks superimposed thereon, a top plate, coil windings spirally wound between alternate pairs of coil forming disks, a metal plate on said top plate, resilient strips peripherally arranged on said top plate and organized to overlie said metallic plate in spaced relation thereto to form a plurality of trimming condensers, a connection from each said coil Winding to a corresponding resilient strip, switch points carried by said bottom plate for selective engagement with said base switch contacts, and connections from the ends of the several coil windings to corresponding switch points.

5. In a. multi-band radio inductance, in combination, a base having switch contacts, an annularly grooved cylindrical coil form turnably mounted thereon, a plurality of spirally wound transformers including a primary and a secondary winding, wound upon said coil form within alternate grooves, a plurality of sets of switch points on said coil form, the points of each set being connected with the Winding ends of a corresponding transformer, and each set of points being selectively engageable with said contacts upon turning of said coil form relative to said base.

6. In a multi-band radio inductance, in combination, a base having switch contacts, an annularly grooved cylindrical coil form turnably mounted thereon, a plurality of spirally wound transformers including a primary and a secondary winding, wound upon said coil form within alternate grooves, a plurality of sets of switch points on said coil form, the points of each set being connected with the winding ends of a corresponding transformer, each set of points being selectively engageable with said contacts upon turning of said coil form relative to said base, and an adjustable trimming condenser for each said transformer carried by and movable with said coil form, said condensers including a single plate common to all.

7. A multi-band radio frequency transformer comprising a central shaft, a plurality of substantially similar insulating spacer washers, and similar coil forming disks, alternately assembled on said shaft in coaxial relation, and transformers comprising primary and secondary wire windings spirally wound between alternate pairs of coil forming disks, the spacer washers over which said windings are wound being substantially the same thickness as a single strand of the wire comprising said windings.

8. In a unitary multiband radio frequency transformer including a plurality of secondary windings, a metal plate having a common connection with one end of each secondary winding, a plurality of metal plates in adjustable capacity relation to said first plate, and conductors connecting said second plates, respectively, with the 

